1. Field of the Invention
Embodiments disclosed herein generally relate to a control mechanism for a downhole tool. Specifically, embodiments disclosed herein relate to a control mechanism and method for actuating or de-actuating a downhole tool by dropping objects, such as drop balls, into a well. More specifically, embodiments disclosed herein relate to a control mechanism for selective actuation of a downhole tool while providing full fluid flow through the downhole tool when the tool is either actuated or de-actuated.
2. Background Art
In the drilling of oil and gas wells, a number of downhole tools function by actuating specific components while being operated in a well borehole. For example, a borehole underreamer or stabilizer may include blocks or blades which may be selectively extended outward from a body of the tool. Specifically, when the underreamer or stabilizer is in a de-actuated or collapsed state, the diameter of the tool is sufficiently small to allow the tool to pass through an existing cased borehole. In contrast, when the underreamer is an actuated or expanded state, the blocks or blades extend from the body of the tool to engage a portion of a borehole. Thus, in the actuated position, the underreamer enlarges the borehole diameter as the tool is rotated and lowered in the borehole. Accordingly, the borehole may be cased with comparatively larger diameter casing than would have been possible otherwise, thereby providing more flow area for the production of oil and gas.
One method of actuating a downhole tool is the application of a specific level of fluid pressure to hydraulic components included in (or connected to) the tool. For example, in the case of an underreamer, the blocks or blades may be extended when fluid pressure is applied to hydraulic cylinders included in the tool. However, one disadvantage to this method is that no other downhole tools which are also actuated by fluid pressure (for example, adjustable stabilizers) may be operated without also operating the underreamer. Thus, in order to use different tools actuated by fluid pressure, the drill string has to be tripped out of the borehole, a first tool is removed from the string, and a second tool is then attached to the drill string. The whole assembly is then tripped back into the borehole. Obviously, this procedure can be costly and time-consuming, especially if the depth of the borehole is in the thousands of feet.
Another method of actuating a downhole tool is the use of drop objects and seats. For example, an underreamer may include a seat configured to receive a drop ball. When the ball is dropped into the well, the ball may travel through the borehole and become seated in the seat, thereby obstructing fluid flow through an inner diameter of the seat. By obstructing the fluid flow, fluid pressure may be applied to hydraulic components within the tool, thus actuating the tool. However, this approach may result in the reduction or stoppage of fluid flow below the tool, which may be required for other drilling operations and/or tools.
Accordingly, there exists a need for an actuation mechanism for actuating and de-actuating a downhole tool while allowing fluid flow below the tool